Thread: Hot Compost

This is how I go about making a hot compost pile from cut grass mowings, with all the rain we get here at this time of year the grass grows pretty quickly, I do let it grow long so I get a good pile of clippings to make a hot compost pile, some pics...
long grass.jpgcut grass.jpgmaking compost.jpgcompleted pile.jpg
The grass is just grass, there's a few weeds and things and of course by letting it go long I get seeds, a lot of them probably aren't mature but the heat from the composting process will kill the seeds so I don't worry too much about seeds. It does take a bit more effort and time to mow when it's long like this but that's the way it is.

Basically I just gather together the mower catcher contents into a pile and/or load up the wheel barrows, I will either water as I mow or in this case I set the water spraying as I make the pile after I have finished mowing, it depends on how dry/wet the clippings are, with this pile the grass was fairly wet/green so I'd rather not have the pile too wet. The bacteria need water to be able to move within the pile but it shouldn't be too wet either, if it's too wet the pile tends towards anaerobic conditions which will smell bad, a slow fine spray is usually adequate, the pile will heat up and the process will start without watering if the pile is just left but after a day or two the pile runs out of water and will definately need watering/turning or the process will stop and you will just have a pile of grass clippings.

The last pic is the completed pile and about a m3 in size, this is about the minimum size as there's enough mat'l within the pile to maintain it's heat, a smaller pile will heat up and if watered and turned will compost but I find it's a short lived process (goes cold quicker) when compared to a larger pile, most likely a volume to surface area relationship, and made worse by winter.
Covering the pile will help keep the moisture and heat in as well as keep rain off which will leach nutrients from the pile and cool it down before it's time and potentially turn things anaerobic.
The pile needs to be turned and watered every couple of days when first built within the first week and then lessening the turnings in the following weeks, I have measured as high as 62°C at the beginning of the process and for a couple of weeks after while the first lot of bacteria do their thing, then the temp will come down into the 40s as another type/s of bacteria moves in for the following weeks until it cools down to ambient, at this point it becomes the job of the fungi/molds and bugs to further break it down.

A few pics of subsequent turnings....
turned pile.jpgturned again.jpg
It only takes a few days for the green to disappear and for the size to start reducing, it starts to look more like horse poo.
The aroma from the pile will tell you if things are going well within the pile or not, if on the first turning (after 1 or 2 days) it stings the eyes (mild) most likely the pile will be offgassing excess nitrogen as ammonia, this could where the grass is very green and no other dry stuff in the mix, if it smells a bit off, the conditions might be anaerobic (without air) and needs to be turned a bit more often or less water or more bulky stuff to stop the grass clumping together, the addition of leaves or shredded trimmings make a better smelling pile and offers a diversity of mat'l, tends to make the pile easier to turn as well.
Once the pile is in it's later stages the need to water is reduced and may only need turning and as soon as it's gone cold it's ready to use.




Pete